U.S. patent number 9,041,617 [Application Number 13/332,193] was granted by the patent office on 2015-05-26 for methods and apparatus for controlling tunable antenna systems.
This patent grant is currently assigned to Apple Inc.. The grantee listed for this patent is Jinku Kim, Qingxiang Li, Matthew A. Mow, Robert S. Sorensen. Invention is credited to Jinku Kim, Qingxiang Li, Matthew A. Mow, Robert S. Sorensen.
United States Patent |
9,041,617 |
Sorensen , et al. |
May 26, 2015 |
Methods and apparatus for controlling tunable antenna systems
Abstract
An electronic device may include an adjustable power supply, at
least one antenna, and associated antenna tuning circuitry. The
antenna tuning circuitry may be an integral part of the antenna and
may include a control circuit and at least one tunable element. The
tunable element may include radio-frequency switches,
continuously/semi-continuously adjustable components such as
tunable resistors, inductors, and capacitors, and other load
circuits that provide desired impedance characteristics. The power
supply may provide power supply voltage signals to the antenna
tuning circuitry via inductive coupling. The power supply voltage
signals may be modulated according to a predetermined lookup table
during device startup so that the control circuit is configured to
generate desired control signals. These control signals adjust the
tunable element so that the antenna can support wireless operation
in desired frequency bands.
Inventors: |
Sorensen; Robert S. (Fremont,
CA), Li; Qingxiang (Mountain View, CA), Mow; Matthew
A. (Los Altos, CA), Kim; Jinku (Cupertino, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Sorensen; Robert S.
Li; Qingxiang
Mow; Matthew A.
Kim; Jinku |
Fremont
Mountain View
Los Altos
Cupertino |
CA
CA
CA
CA |
US
US
US
US |
|
|
Assignee: |
Apple Inc. (Cupertino,
CA)
|
Family
ID: |
47436161 |
Appl.
No.: |
13/332,193 |
Filed: |
December 20, 2011 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20130154897 A1 |
Jun 20, 2013 |
|
Current U.S.
Class: |
343/850; 343/861;
343/745 |
Current CPC
Class: |
H01Q
23/00 (20130101); H03J 3/20 (20130101); H01Q
5/314 (20150115); H01Q 7/005 (20130101); H01Q
5/335 (20150115); H04B 1/40 (20130101); H01Q
5/328 (20150115); H03J 2200/11 (20130101) |
Current International
Class: |
H01Q
1/50 (20060101) |
Field of
Search: |
;343/850,861,745 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1754313 |
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Mar 2006 |
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CN |
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202978926 |
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Jun 2013 |
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CN |
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2456206 |
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Aug 1976 |
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DE |
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0021762 |
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Jan 1981 |
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EP |
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1630960 |
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Mar 2006 |
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EP |
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2463536 |
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Mar 2010 |
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GB |
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201025730 |
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Jul 2010 |
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TW |
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Other References
Parameswaran Sivalingam, et al. "Electronically Tunable Monopole
Antenna Using Selective Capacitance Loading", Motorola, Inc., Apr.
15, 2008. cited by applicant.
|
Primary Examiner: Levi; Dameon E
Assistant Examiner: Dawkins; Collin
Attorney, Agent or Firm: Treyz Law Group Tsai; Jason Guihan;
Joseph F.
Claims
What is claimed is:
1. An antenna in an electronic device comprising: an antenna feed
that includes first and second antenna feed terminals; a control
circuit configured to receive a first control signal from the
antenna feed and configured to generate a second control signal; an
antenna tuning element having a first terminal coupled to the first
antenna feed terminal, a second terminal coupled to the second
antenna feed terminal, and a third terminal configured to receive
the second control signal; a voltage regulating circuit in the
control circuit; a comparator circuit in the control circuit; and a
counter circuit in the control circuit that has a control input
that is coupled to the comparator circuit and has an output on
which the second control signal is provided, wherein the counter
circuit is configured to increment its count in response to
detecting a transition at its control input, the second control
signal at the output of the counter circuit is proportional to the
count associated with the counter circuit, and the antenna tuning
element is placed in an operating state to tune the antenna to a
selected frequency based on the count as identified by the second
control signal.
2. The antenna defined in claim 1 further comprising: antenna
resonating structures coupled to the antenna feed via at least a
capacitor, wherein the first and second terminals of the antenna
tuning element is coupled to the first and second antenna feed
terminals via respective inductors.
3. The antenna defined in claim 1, wherein the voltage regulating
circuit receives the first control signal and generates
corresponding first and second voltage signals.
4. The antenna defined in claim 3, wherein the comparator circuit
receives the first and second voltage signals, drives its output
high when the first voltage signal exceeds the second voltage
signal, and drives its output low when the second voltage signal
exceeds the first voltage signal.
5. The antenna defined in claim 1, wherein the antenna tuning
element comprises radio-frequency switching circuitry.
6. The antenna defined in claim 5, wherein the antenna tuning
element further comprises a plurality of capacitive structures
couple to respective ports of the radio-frequency switching
circuitry.
7. The antenna defined in claim 5, wherein the antenna tuning
element further comprises a plurality of inductive structures
coupled to respective ports of the radio-frequency switching
circuitry.
8. The antenna defined in claim 1, wherein the antenna tuning
element comprises a variable capacitor.
9. The antenna defined in claim 1 wherein the antenna comprises an
antenna selected from the group consisting of: a loop antenna, an
inverted-F antenna, a patch antenna, a slot antenna, a planar
inverted-F antenna, and a helical antenna.
10. A method for using an electronic device having control
circuitry, transceiver circuitry, and an antenna, wherein the
antenna is coupled to the transceiver circuitry via first and
second antenna feed lines, the control circuitry has first and
second terminals, the first terminal is coupled directly to the
first antenna feed line via a first inductor, the second terminal
is coupled directly to the second antenna feed line via a second
inductor, and the antenna includes at least one antenna tuning
circuit, the method comprising: with the control circuitry, tuning
the antenna to operate in a desired frequency band by supplying a
control signal to the antenna tuning circuit via the first antenna
feed line, wherein the control circuitry toggles the control signal
a predetermined number of times and the antenna tuning circuit
includes a counter circuit; and with the counter circuit,
determining an amount by which the antenna is to be tuned by
counting the number of times the control signal toggles.
11. The method defined in claim 10, wherein supplying the control
signal to the antenna tuning circuit via the first antenna feed
line comprises supplying the control signal to the antenna tuning
circuit via the first antenna feed line during power-on-reset
operations.
12. The method defined in claim 10 further comprising: with the
control circuitry, supplying a power supply signal to the antenna
tuning circuit via the first antenna feed line during normal
operation.
13. The method defined in claim 10, wherein the antenna tuning
circuit includes a control circuit and a tunable element, and
wherein supplying the control signal to the antenna tuning circuit
comprises configuring the control circuit to generate an additional
control signal that adjusts the tunable element.
14. An antenna in an electronic device comprising: an antenna feed
that includes first and second antenna feed terminals; a control
circuit configured to receive a first control signal from the
antenna feed and configured to generate a second control signal; an
antenna tuning element having a first terminal coupled to the first
antenna feed terminal, a second terminal coupled to the second
antenna feed terminal, and a third terminal configured to receive
the second control signal; a voltage regulating circuit in the
control circuit that receives the first control signal and
generates corresponding first and second voltage signals and a
power supply voltage; a comparator circuit in the control circuit
that is powered by the power supply voltage; and a counter circuit
in the control circuit that is configured to start its count when
the power supply voltage is above a predetermined threshold and
increment its count in response to detecting a transition at its
control input, wherein the antenna tuning element is placed in an
operating state to tune the antenna to a selected frequency based
on the count of the counter circuit.
Description
BACKGROUND
This relates generally to wireless communications circuitry, and
more particularly, to electronic devices that have wireless
communications circuitry.
Electronic devices such as portable computers and cellular
telephones are often provided with wireless communications
capabilities. For example, electronic devices may use long-range
wireless communications circuitry such as cellular telephone
circuitry to communicate using cellular telephone bands. Electronic
devices may use short-range wireless communications circuitry such
as wireless local area network communications circuitry to handle
communications with nearby equipment. Electronic devices may also
be provided with satellite navigation system receivers and other
wireless circuitry.
To satisfy consumer demand for small form factor wireless devices,
manufacturers are continually striving to implement wireless
communications circuitry such as antenna components using compact
structures. However, it can be difficult to fit conventional
antenna structures into small devices. For example, antennas that
are confined to small volumes often exhibit narrower operating
bandwidths than antennas that are implemented in larger volumes. If
the bandwidth of an antenna becomes too small, the antenna will not
be able to cover all communications bands of interest.
In view of these considerations, it would be desirable to provide
improved wireless circuitry for electronic devices.
SUMMARY
A wireless electronic device may include storage and processing
circuitry and wireless communications circuitry. The wireless
communications circuitry may include a baseband processor,
transceiver circuitry, and at least one antenna. The transceiver
circuitry may be coupled to the antenna via a transmission line
having a signal path and a ground path. The signal path may be
coupled to a positive antenna feed terminal while the ground path
may be coupled to a ground antenna feed terminal.
The antenna may include an antenna resonating element and at least
one antenna tuning circuit. The antenna resonating element may be
coupled to the signal path via a capacitor, whereas the antenna
tuning circuit may be coupled to the signal path via an inductor.
The storage and processing circuitry may couple a device power
supply voltage onto the signal and ground paths via inductive
circuits. Configured in this way, radio-frequency signals may be
conveyed between the transceiver circuitry and the antenna
resonating element while the device power supply voltage signal may
be passed to the antenna tuning circuit.
The antenna tuning circuit may include a control circuit and a
tunable element. The antenna tuning circuit may include a voltage
regulator, a comparator, a low-pass filter, and a counter. The
voltage regulator may be capable of generating a first fixed
voltage signal that is lower in magnitude compared to the device
power supply voltage signal, a second voltage signal that is a
scale-down version of the device power supply voltage signal, and a
third reference voltage signal that is lower in magnitude compared
to the first voltage signal. The second and third voltage signals
may be fed to first and second inputs of the comparator,
respectively. The comparator may be configured to drive its output
high when the second voltage signal exceeds the third voltage
signal and may be configured to drive its output low when the third
voltage signal exceeds the second voltage signal.
The output of the comparator may be coupled to a control input of
the counter. The counter may count up in response to detecting a
rising transition at its control input (as an example). The counter
may also have a reset input operable to receive a low-pass filtered
version of the first voltage signal (e.g., the reset input of the
counter may receive the first voltage signal via the low-pass
filter). The counter may generate a control signal reflective of
its current count value. The control signal may be used directly in
adjusting tunable element. The tunable element may include
radio-frequency switches, continuously or semi-continuously tunable
resistive/inductive/capacitive components forming using integrated
circuits, discrete surface mount components, or other suitable
conductive structures, and other load circuits configured to
provide desired impedance characteristics for the antenna at
selected frequencies.
The control circuit may be configured by modulating the power
supply voltage signal according to a predetermined scheme during
startup (e.g., during power-on-reset operations). For example, the
power supply voltage signal may be toggled a given number of times
between first and second positive voltage levels to trigger counter
to count up to a desired number. The number of time the counter
increments may be determined based on the desired operating
frequency band of the wireless device. For example, the counter may
be configured to exhibit a count of four so that antenna can
support wireless operation in a first set of frequency bands or may
be configured to exhibit a count of six so that antenna can support
wireless operation in a second set of frequency bands that is
different than the first set of frequency bands. The required count
number corresponding to the different frequency bands may be
tabulated in a precomputed list that is stored in the storage and
processing circuitry of the device. By using an antenna tuning
scheme of this type, the antenna may be able to cover a wider range
of communications frequencies than would otherwise be possible.
Further features of the present invention, its nature and various
advantages will be more apparent from the accompanying drawings and
the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an illustrative electronic device
with wireless communications circuitry in accordance with an
embodiment of the present invention.
FIG. 2 is a diagram showing how radio-frequency transceiver
circuitry may be coupled to one or more antennas within an
electronic device of the type shown in FIG. 1 in accordance with an
embodiment of the present invention.
FIG. 3 is a circuit diagram showing how an antenna in the
electronic device of FIG. 1 may be coupled to radio-frequency
transceiver circuitry in accordance with an embodiment of the
present invention.
FIG. 4 is plot showing trade-offs between antenna gain and antenna
bandwidth for a given antenna volume.
FIG. 5 is a schematic diagram of an illustrative series-fed loop
antenna that may be used in an electronic device in accordance with
an embodiment of the present invention.
FIG. 6 is a schematic diagram of an illustrative parallel-fed loop
antenna containing antenna tuning circuitry in accordance with an
embodiment of the present invention.
FIG. 7A is a schematic diagram of an illustrative inverted-F
antenna that may be used in an electronic device in accordance with
an embodiment of the present invention.
FIGS. 7B and 7C are schematic diagrams of an illustrative
inverted-F antenna containing an antenna tuning circuit in
accordance with an embodiment of the present invention.
FIG. 8 is a schematic diagram of an illustrative inverted-F antenna
containing antenna tuning circuitry in accordance with an
embodiment of the present invention.
FIGS. 9 and 10 are plots showing how antennas containing tuning
circuitry may be used to cover multiple communications bands of
interest in accordance with an embodiment of the present
invention.
FIG. 11 is a diagram showing how an antenna containing antenna
tuning circuitry may be coupled to radio-frequency transceiver
circuitry in accordance with an embodiment of the present
invention.
FIG. 12 is a circuit diagram of illustrative antenna tuning
circuitry that includes a control circuit and a tunable element in
accordance with an embodiment of the present invention.
FIG. 13 is a timing diagram illustrating the operation of the
antenna tuning circuitry of the type shown in FIG. 12 in accordance
with an embodiment of the present invention.
FIG. 14 is an illustrative lookup table containing predetermined
control information corresponding to different operating
frequencies in accordance with an embodiment of the present
invention.
FIGS. 15 and 16 are circuit diagrams of illustrative switchable
load circuits that may be used as the tunable element in the
antenna tuning circuitry of FIG. 12 in accordance with an
embodiment of the present invention.
FIG. 17 is a circuit diagram of an illustrative variable capacitor
circuit that may be used as the tunable element in the antenna
tuning circuitry of FIG. 12 in accordance with an embodiment of the
present invention.
FIG. 18 is a flow chart of illustrative steps for using the antenna
tuning circuitry of the type shown in connection with FIG. 12 to
cover multiple communications bands of interest in accordance with
an embodiment of the present invention.
DETAILED DESCRIPTION
Electronic devices such as device 10 of FIG. 1 may be provided with
wireless communications circuitry. The wireless communications
circuitry may be used to support long-range wireless communications
such as communications in cellular telephone bands. Examples of
long-range (cellular telephone) bands that may be handled by device
10 include the 800 MHz band, the 850 MHz band, the 900 MHz band,
the 1800 MHz band, the 1900 MHz band, the 2100 MHz band, the 700
MHz band, and other bands. The long-range bands used by device 10
may include the so-called LTE (Long Term Evolution) bands. The LTE
bands are numbered (e.g., 1, 2, 3, etc.) and are sometimes referred
to as E-UTRA operating bands. Long-range signals such as signals
associated with satellite navigation bands may be received by the
wireless communications circuitry of device 10. For example, device
10 may use wireless circuitry to receive signals in the 1575 MHz
band associated with Global Positioning System (GPS)
communications. Short-range wireless communications may also be
supported by the wireless circuitry of device 10. For example,
device 10 may include wireless circuitry for handling local area
network links such as WiFi.RTM. links at 2.4 GHz and 5 GHz,
Bluetooth.RTM. links at 2.4 GHz, etc.
As shown in FIG. 1, device 10 may include storage and processing
circuitry 28. Storage and processing circuitry 28 may include
storage such as hard disk drive storage, nonvolatile memory (e.g.,
flash memory or other electrically-programmable-read-only memory
configured to form a solid state drive), volatile memory (e.g.,
static or dynamic random-access-memory), etc. Processing circuitry
in storage and processing circuitry 28 may be used to control the
operation of device 10. This processing circuitry may be based on
one or more microprocessors, microcontrollers, digital signal
processors, application specific integrated circuits, etc.
Storage and processing circuitry 28 may be used to run software on
device 10, such as internet browsing applications,
voice-over-internet-protocol (VOIP) telephone call applications,
email applications, media playback applications, operating system
functions, functions related to communications band selection
during radio-frequency transmission and reception operations, etc.
To support interactions with external equipment such as base
station 21, storage and processing circuitry 28 may be used in
implementing communications protocols. Communications protocols
that may be implemented using storage and processing circuitry 28
include internet protocols, wireless local area network protocols
(e.g., IEEE 802.11 protocols--sometimes referred to as WiFi.RTM.),
protocols for other short-range wireless communications links such
as the Bluetooth.RTM. protocol, IEEE 802.16 (WiMax) protocols,
cellular telephone protocols such as the "2G" Global System for
Mobile Communications (GSM) protocol, the "2G" Code Division
Multiple Access (CDMA) protocol, the "3G" Universal Mobile
Telecommunications System (UMTS) protocol, and the "4G" Long Term
Evolution (LTE) protocol, MIMO (multiple input multiple output)
protocols, antenna diversity protocols, etc. Wireless
communications operations such as communications band selection
operations may be controlled using software stored and running on
device 10 (i.e., stored and running on storage and processing
circuitry 28 and/or input-output circuitry 30).
Input-output circuitry 30 may include input-output devices 32.
Input-output devices 32 may be used to allow data to be supplied to
device 10 and to allow data to be provided from device 10 to
external devices. Input-output devices 32 may include user
interface devices, data port devices, and other input-output
components. For example, input-output devices may include touch
screens, displays without touch sensor capabilities, buttons,
joysticks, click wheels, scrolling wheels, touch pads, key pads,
keyboards, microphones, cameras, buttons, speakers, status
indicators, light sources, audio jacks and other audio port
components, digital data port devices, light sensors, motion
sensors (accelerometers), capacitance sensors, proximity sensors,
etc.
Input-output circuitry 30 may include wireless communications
circuitry 34 for communicating wirelessly with external equipment.
Wireless communications circuitry 34 may include radio-frequency
(RF) transceiver circuitry formed from one or more integrated
circuits, power amplifier circuitry, low-noise input amplifiers,
passive RF components, one or more antennas, transmission lines,
and other circuitry for handling RF wireless signals. Wireless
signals can also be sent using light (e.g., using infrared
communications).
Wireless communications circuitry 34 may include radio-frequency
transceiver circuitry 90 for handling various radio-frequency
communications bands. For example, circuitry 90 may include
transceiver circuitry 36, 38, and 42. Transceiver circuitry 36 may
handle 2.4 GHz and 5 GHz bands for WiFi.RTM. (IEEE 802.11)
communications and may handle the 2.4 GHz Bluetooth.RTM.
communications band. Circuitry 34 may use cellular telephone
transceiver circuitry 38 for handling wireless communications in
cellular telephone bands such as at 850 MHz, 900 MHz, 1800 MHz,
1900 MHz, and 2100 MHz and/or the LTE bands and other bands (as
examples). Circuitry 38 may handle voice data and non-voice data
traffic.
Transceiver circuitry 90 may include global positioning system
(GPS) receiver equipment such as GPS receiver circuitry 42 for
receiving GPS signals at 1575 MHz or for handling other satellite
positioning data. In WiFi.RTM. and Bluetooth.RTM. links and other
short-range wireless links, wireless signals are typically used to
convey data over tens or hundreds of feet. In cellular telephone
links and other long-range links, wireless signals are typically
used to convey data over thousands of feet or miles.
Wireless communications circuitry 34 may include one or more
antennas 40. Antennas 40 may be formed using any suitable antenna
types. For example, antennas 40 may include antennas with
resonating elements that are formed from loop antenna structure,
patch antenna structures, inverted-F antenna structures, slot
antenna structures, planar inverted-F antenna structures, helical
antenna structures, hybrids of these designs, etc. Different types
of antennas may be used for different bands and combinations of
bands. For example, one type of antenna may be used in forming a
local wireless link antenna and another type of antenna may be used
in forming a remote wireless link antenna.
As shown in FIG. 1, wireless communications circuitry 34 may also
include baseband processor 88. Baseband processor may include
memory and processing circuits and may also be considered to form
part of storage and processing circuitry 28 of device 10.
Baseband processor 88 may provide data to storage and processing
circuitry 28 via path 87. The data on path 87 may include raw and
processed data associated with wireless (antenna) performance
metrics for received signals such as received power, transmitted
power, frame error rate, bit error rate, channel quality
measurements based on received signal strength indicator (RSSI)
information, channel quality measurements based on received signal
code power (RSCP) information, channel quality measurements based
on reference symbol received power (RSRP) information, channel
quality measurements based on signal-to-interference ratio (SINR)
and signal-to-noise ratio (SNR) information, channel quality
measurements based on signal quality data such as Ec/Io or Ec/No
data, information on whether responses (acknowledgements) are being
received from a cellular telephone tower corresponding to requests
from the electronic device, information on whether a network access
procedure has succeeded, information on how many re-transmissions
are being requested over a cellular link between the electronic
device and a cellular tower, information on whether a loss of
signaling message has been received, information on whether paging
signals have been successfully received, and other information that
is reflective of the performance of wireless circuitry 34. This
information may be analyzed by storage and processing circuitry 28
and/or processor 88 and, in response, storage and processing
circuitry 28 (or, if desired, baseband processor 58) may issue
control commands for controlling wireless circuitry 34. For
example, baseband processor 88 may issue commands on path 89 that
direct transceiver circuitry 90 to switch into use desired
transmitters/receivers and antennas.
Antenna diversity schemes may be implemented in which multiple
redundant antennas are used in handling communications for a
particular band or bands of interest. In an antenna diversity
scheme, storage and processing circuitry 28 may select which
antenna to use in real time based on signal strength measurements
or other data. In multiple-input-multiple-output (MIMO) schemes,
multiple antennas may be used in transmitting and receiving
multiple data streams, thereby enhancing data throughput.
Illustrative locations in which antennas 40 may be formed in device
10 are shown in FIG. 2. As shown in FIG. 2, electronic device 10
may have a housing such as housing 12. Housing 12 may include
plastic walls, metal housing structures, structures formed from
carbon-fiber materials or other composites, glass, ceramics, or
other suitable materials. Housing 12 may be formed using a single
piece of material (e.g., using a unibody configuration) or may be
formed from a frame, housing walls, and other individual parts that
are assembled to form a completed housing structure. The components
of device 10 that are shown in FIG. 1 may be mounted within housing
12. Antenna structures 40 may be mounted within housing 12 and may,
if desired, be formed using parts of housing 12. For example,
housing 12 may include metal housing sidewalls, peripheral
conductive members such as band-shaped members (with or without
dielectric gaps), conductive bezels, and other conductive
structures that may be used in forming antenna structures 40.
As shown in FIG. 2, antenna structures 40 may be coupled to
transceiver circuitry 90 by paths such as paths 45. Paths 45 may
include transmission line structures such as coaxial cables,
microstrip transmission lines, stripline transmission lines, etc.
Impedance matching circuitry, filter circuitry, and switching
circuitry may be interposed in paths 45 (as examples). Impedance
matching circuitry may be used to ensure that antennas 40 are
efficiently coupled to transceiver circuitry 90 in desired
frequency bands of interest. Filter circuitry may be used to
implement frequency-based multiplexing circuits such as diplexers,
duplexers, and triplexers. Switching circuitry may be used to
selectively couple antennas 40 to desired ports of transceiver
circuitry 90. For example, a switch may be configured to route one
of paths 45 to a given antenna in one operating mode. In another
operating mode, the switch may be configured to route a different
one of paths 45 to the given antenna. The use of switching
circuitry between transceiver circuitry 90 and antennas 40 allows
device 10 to switch particular antennas 40 in and out of use
depending on the current performance associated with each of the
antennas.
In a device such as a cellular telephone that has an elongated
rectangular outline, it may be desirable to place antennas 40 at
one or both ends of the device. As shown in FIG. 2, for example,
some of antennas 40 may be placed in upper end region 42 of housing
12 and some of antennas 40 may be placed in lower end region 44 of
housing 12. The antenna structures in device 10 may include a
single antenna in region 42, a single antenna in region 44,
multiple antennas in region 42, multiple antennas in region 44, or
may include one or more antennas located elsewhere in housing
12.
Antenna structures 40 may be formed within some or all of regions
such as regions 42 and 44. For example, an antenna such as antenna
40T-1 may be located within region 42-1 or an antenna such as
antenna 40T-2 may be formed that fills some or all of region 42-2.
Similarly, an antenna such as antenna 40B-1 may fill some or all of
region 44-2 or an antenna such as antenna 40B-2 may be formed in
region 44-1. These types of arrangements need not be mutually
exclusive. For example, region 44 may contain a first antenna such
as antenna 40B-1 and a second antenna such as antenna 40B-2.
Transceiver circuitry 90 may contain transmitters such as
radio-frequency transmitters 48 and receivers such as
radio-frequency receivers 50. Transmitters 48 and receivers 50 may
be implemented using one or more integrated circuits (e.g.,
cellular telephone communications circuits, wireless local area
network communications circuits, circuits for Bluetooth.RTM.
communications, circuits for receiving satellite navigation system
signals, power amplifier circuits for increasing transmitted signal
power, low noise amplifier circuits for increasing signal power in
received signals, other suitable wireless communications circuits,
and combinations of these circuits).
FIG. 3 is a diagram showing how radio-frequency path 45 may be used
to convey radio-frequency signals between an antenna 40 and
radio-frequency transceiver 91. Antenna 40 may be one of the
antennas of FIG. 2 (e.g., antenna, 40T-1, 40T-2, 40B-1, 40B-2, or
other antennas). Radio-frequency transceiver 91 may be a receiver
and/or transmitter in transceiver circuitry 90, wireless local area
network transceiver 36 (e.g., a transceiver operating at 2.4 GHz, 5
GHz, 60 GHz, or other suitable frequency), cellular telephone
transceiver 38, or other radio-frequency transceiver circuitry for
receiving and/or transmitting radio-frequency signals.
Conductive path 45 may include one or more transmission lines such
as one or more segments of coaxial cable, one or more segments of
microstrip transmission line, one or more segments of stripline
transmission line, or other transmission line structures. Path 45
may include a first conductor such as signal line 45A and may
include a second conductor such as ground line 45B. Antenna 40 may
have an antenna feed with a positive antenna feed terminal 58 (+)
that is coupled to signal path 45A and a ground antenna feed
terminal 54 (-) that is coupled to ground path 45B. If desired,
circuitry such as filters, impedance matching circuits, switches,
amplifiers, and other radio-frequency circuits may be interposed
within path 45.
Antenna 40 of FIG. 3 may be capable of supporting wireless
communications in a first set of radio-frequency bands. For
example, antenna 40 may be operable in a lower frequency band that
covers the GSM sub-bands at 850 MHz and 900 MHz and a higher
frequency band that covers the GSM sub-bands at 1800 MHz and 1900
MHz and the data sub-band at 2100 MHz.
It may be desirable for device 10 to be able to support other
wireless communications bands in addition to the first set of
radio-frequency bands. For example, it may be desirable for antenna
40 to be capable of operating in a higher frequency band that
covers the GSM sub-bands at 1800 MHz and 1900 MHz and the data
sub-band at 2100 MHz, a first lower frequency band that covers the
GSM sub-bands at 850 MHz and 900 MHz, and a second lower frequency
band that covers the LTE band at 700 MHz, the GSM sub-bands at 710
MHz and 750 MHz, the UMTS sub-band at 700 MHz, and other desired
wireless communications bands.
The band coverage of antenna 40 may be limited by its volume (i.e.,
the amount of space that is occupied by antenna 40 within housing
12). In general, for an antenna having a given volume, a higher
band coverage (or bandwidth) results in a decrease in gain (e.g.,
the product of maximum gain and bandwidth is constant).
FIG. 4 is a graph showing how antenna gain varies as a function of
antenna bandwidth for a loop antenna (as an example). Curve 200
represents a gain-bandwidth characteristic for a first loop antenna
having a first volume, whereas curve 202 represents a
gain-bandwidth characteristic for a second loop antenna having a
second volume that is greater than the first volume. As shown in
FIG. 4, the first loop antenna can provide bandwidth BW1 while
exhibiting gain g.sub.0 (point 204). In order to provide more
bandwidth (i.e., bandwidth BW2) with the first loop antenna, the
gain of the first loop antenna would be lowered to gain g.sub.1
(point 205).
One way of providing more band coverage is to increase the volume
of the loop antenna. For example, the second loop antenna having a
greater volume than the volume of the first loop antenna is capable
of providing bandwidth BW2 while exhibiting g.sub.0 (point 206).
Increasing the volume of loop antennas, however, may not always be
feasible if a small form factor is desired.
To satisfy consumer demand for small form factor wireless devices,
one or more of antennas 40 may be provided with antenna tuning
circuitry. The tuning circuitry may include, for example, switching
circuitry based on one or more switches or continuously tunable
load components. The switching circuitry may, for example, include
a switch that can be placed in an open or closed position. When the
switch is placed in its open position, an antenna may exhibit a
first frequency response. When the switch is placed in its closed
position, the antenna may exhibit a second frequency response. By
using an antenna tuning scheme of this type, antennas 40 may be
able to cover a wider range of communications frequencies than
would otherwise be possible. The use of tuning for antennas 40 may
allow a relatively narrow bandwidth (and potentially compact)
design to be used, if desired.
The way in which antenna 40 operates may be understood with
reference to FIGS. 5-18, which show how antenna 40 of FIG. 3 may be
implemented by adding antenna tuning circuitry antenna 40.
In one suitable embodiment of the present invention, antenna 40 may
be a loop antenna. FIG. 5 is a schematic diagram of a series-fed
loop antenna that may be used in device 10. As shown in FIG. 5,
series-fed loop antenna 40 may have a loop-shaped conductive path
such as loop 84. Transmission line TL may include positive signal
conductor 45A and ground conductor 45B. Paths 45A and 45B may be
contained in coaxial cables, micro-strip transmission lines on flex
circuits and/or rigid printed circuit boards, etc. Transmission
line TL may be coupled to the feed of antenna 40 using positive
antenna feed terminal 58 and ground antenna feed terminal 54.
It may be challenging to use a series-fed feed arrangement of the
type shown in FIG. 5 to feed a multi-band loop antenna. For
example, it may be desired to operate a loop antenna in a lower
frequency band that covers the GSM sub-bands at 850 MHz and 900 MHz
and a higher frequency band that covers the GSM sub-bands at 1800
MH and 1900 MHz and the data sub-band at 2100 MHz. This type of
arrangement may be considered to be a dual band arrangement (e.g.,
850/900 for the first band and 1800/1900/2100 for the second band)
or may be considered to have five bands (850, 900, 1800, 1900, and
2100). In multi-band arrangements such as these, series-fed
antennas such as loop antenna 82 of FIG. 5 may exhibit
substantially better impedance matching in the high-frequency
communications band than in the low-frequency communications
band.
A more satisfactory level of performance may be obtained using a
parallel-fed arrangement with appropriate impedance matching
features. An illustrative parallel-fed loop antenna is shown
schematically in FIG. 6. As shown in FIG. 6, parallel-fed loop
antenna 40 may have a loop of conductor such as loop 85. Loop 85 in
the FIG. 6 example is shown as being circular. This is merely
illustrative. Loop 85 may have other shapes if desired (e.g.,
rectangular shapes, shapes with both curved and straight sides,
shapes with irregular borders, etc.).
An antenna tuning circuit such as tuning circuit 100-1 may bridge
terminals 58 and 54, thereby "closing" the loop formed by path 85.
In such an arrangement, a capacitive circuit may be interposed in
loop 85 so that antenna feed terminals 58 and 54 are not shorted
together at low frequencies. If desired, additional antenna tuning
circuits such as antenna tuning circuits 100-2 and 100-3 may be
interposed in loop 85 in the parallel-fed loop antenna of FIG. 6.
For example, tuning circuit 100-1 may be a switchable impedance
matching circuit, whereas circuit 100-2 may be a continuously
adjustable variable capacitor. The impedance of parallel-fed loop
antenna 40 of FIG. 6 may be adjusted by proper tuning/selection of
circuits 100 (e.g., antenna tuning circuits 100-1, 100-2, and
100-3). In general, antenna 40 may include any number of antenna
tuning circuits 100 to provide desired flexibility/tunability.
In another suitable embodiment of the present invention, antenna 40
may be an inverted-F antenna. FIG. 7A is a schematic diagram of an
inverted-F antenna that may be used in device 10. As shown in FIG.
7A, inverted-F antenna 40 may have an antenna resonating element
such as antenna resonating element 41 and a ground structure such
as ground G. Antenna resonating element 41 may have a main
resonating element arm such as arm 96. Short circuit branch such as
shorting path 94 may couple arm 96 to ground G. An antenna feed may
contain positive antenna feed terminal 58 (+) and ground antenna
feed terminal 54 (-). Positive antenna feed terminal 58 may be
coupled to arm 96, whereas ground antenna feed terminal 54 may be
coupled to ground G. Arm 96 in the FIG. 7A example is shown as
being a single straight segment. This is merely illustrative. Arm
96 may have multiple bends with curved and/or straight segments, if
desired.
In one suitable arrangement of the present invention, resonating
element 41 of inverted-F antenna 40 may include an antenna tuning
circuit 100 interposed in shorting path 94 (see, e.g., FIG. 7B). In
the example of FIG. 7B, antenna tuning circuit 100 may be a
switchable impedance matching network, a switchable inductive
network, a continuously tunable capacitive circuit, etc. In yet
another suitable arrangement of the present invention, resonating
element 41 of inverted-F antenna 40 may include an antenna tuning
circuit 100 coupled between the extended portion of resonating arm
96 and ground G (see, e.g., FIG. 7C). In such an arrangement, a
capacitive structure such as capacitor 295 may be interposed in
shorting path 94 so that antenna tuning circuit 100 is not shorted
to ground at low frequencies. In the example of FIG. 7C, antenna
tuning circuit may be a switchable inductor, a continuously tunable
capacitive/resistive circuit, etc.
In general, inverted-F antenna 40 may include any number of antenna
tuning circuits 100. As shown in FIG. 8, short circuit branch 94
may include at least one tuning circuit that couples arm 96 to
ground. For example, tuning circuits 100-4 and 100-5 may be
interposed in short circuit path 94. Tuning circuits 100-4 and
100-5 may be switchable inductive paths, as an example (e.g., at
least one of tuning circuits 100-4 and 100-5 may be activated to
short arm 96 to ground). If desired, antenna tuning circuit 100-6
may be coupled in parallel with the antenna feed between positive
antenna feed terminal 58 and ground feed terminal 54. Tuning
circuit 100-6 may be an adjustable impedance matching network
circuit, as an example.
As another example, antenna tuning circuit 100-7 may be interposed
in the antenna resonating arm 96. An additional tuning circuit such
as tuning circuit 100-8 may also be coupled in parallel with
antenna tuning circuit 100-7. Antenna tuning circuit 100-7 may be a
continuously adjustable variable capacitor, whereas circuit 100-8
may be a switchable inductor (as examples). If desired, additional
tuning circuits such as antenna tuning circuits 100-9 and 100-10
(e.g., continuously tunable or semi-continuously tunable
capacitors, switchable inductors, etc.) may be coupled between the
extended portion of arm 96 to ground G.
The placement of these tuning circuits 100 in FIGS. 7 and 8 is
merely illustrative and do not serve to limit the scope of the
present invention. Additional capacitors and/or inductors may be
added to ensure that each antenna tuning circuit 100 is not shorted
circuited to ground at low frequencies (e.g., frequencies below 100
MHz). In general, antennas 40 may include antennas with resonating
elements that are formed from loop antenna structures, patch
antenna structures, inverted-F antenna structures, slot antenna
structures, planar inverted-F antenna structures, helical antenna
structures, hybrids of these designs, etc. At least a portion of
antennas 40 in device 10 may contain at least one antenna tuning
circuit 100 (formed at any suitable location on the antenna) that
can be adjusted so that wireless circuitry 34 may be able to cover
the desired range of communications frequencies.
By dynamically controlling antenna tuning circuits 100, antenna 40
may be able to cover a wider range of communications frequencies
than would otherwise be possible. A standing-wave-ratio (SWR)
versus frequency plot such as SWR plot of FIG. 9 illustrates the
band tuning capability for antenna 40. As shown in FIG. 9, solid
SWR frequency characteristic curve 124 corresponds to a first
antenna tuning mode in which antenna 40 exhibits satisfactory
resonant peaks at low-band frequency f.sub.A (e.g., to cover the
850 MHz band) and high-band frequency f.sub.B (e.g., to cover the
1900 MHz band). In the first antenna tuning mode, the antenna
tuning circuits 100 of antenna 40 may be placed in a first
configuration (e.g., antenna tuning circuits 100 may be provided
with a first set of control signals).
Dotted SWR frequency characteristic curve 126 corresponds to a
second antenna tuning mode in which the antennas of device 10
exhibits satisfactory resonant peaks at low-band frequency f.sub.A'
(e.g., to cover the 750 MHz band) and high-band frequency f.sub.B'
(e.g., to cover the 2100 MHz band). In the second antenna tuning
mode, the antenna tuning circuits 100 may be placed in a second
configuration that is different than the first configuration (e.g.,
antenna tuning circuits 100 may be provided with a second set of
control signals that is different than the first set of control
signals).
If desired, antenna 40 may be placed in a third antenna tuning mode
in which antenna 40 exhibits satisfactory resonant peaks at both
low-band frequencies f.sub.A' and f.sub.A (e.g., to cover both the
750 and 850 MHz bands) and at high-band frequencies f.sub.B and
f.sub.B' (e.g., to cover both the 1900 and 2100 MHz bands), as
shown by SWR characteristic curve 128. In the third antenna tuning
mode, the antenna tuning circuits 100 may be placed in a third
configuration that is different than the first and second
configurations (e.g., antenna tuning circuits 100 may be provided
with a third set of control signals that is different than the
first and second sets of control signals). A combination of tuning
methods may be used so that the resonance curve 128 exhibits
broader frequency ranges than curves 124 and 126.
In another suitable arrangement, antenna 40 may be placed in a
fourth antenna tuning mode in which antenna 40 exhibits
satisfactory resonant peaks at mid-band frequencies f.sub.c and
f.sub.D (e.g., to cover frequencies between the low and high
bands), as shown by SWR characteristic curve 130 of FIG. 10. In the
fourth antenna tuning mode, the antenna tuning circuits 100 may yet
be placed in another different configuration. The SWR curves of
FIGS. 9 and 10 are merely illustrative and do not serve to limit
the scope of the present invention. In general, antenna(s) 40 may
include antenna tuning circuits 100 that enable device 10 to
transmit and receive wireless signals in any suitable number of
radio-frequency communications bands.
Antenna tuning circuits 100 may be formed as an integral part of
antenna 40. In such arrangements, there needs to be a way for
storage and processing circuitry 28 to adjust each tuning circuit
100 prior to normal wireless operation. Because tuning circuits 100
can include active circuits such as radio-frequency switches,
tuning circuits 100 may also need to be provided with power supply
voltages. As described previously in connection with FIG. 3,
antenna 40 may be coupled to radio-frequency transceiver 91 via
signal path 45A and ground path 45B. Storage and processing circuit
28 (sometimes referred to herein as control circuitry) may couple
direct current (DC) voltage signal V1 onto path 45 via inductors
293 (see, e.g., FIG. 11). Signal V1 may be varied in time using
storage and processing circuitry 28 and/or baseband processor 88
and may therefore sometimes be referred to as a control signal.
Signal path 45A may be coupled to antenna resonating element 41 of
antenna 40 via capacitive circuit 294 and may be coupled to antenna
tuning circuit 100 via an inductive circuit 296. Capacitor 294
serves to pass only radio-frequency signals (sometimes referred to
as alternating current "small" signals) to antenna resonating
element 41, whereas inductor 296 serves to pass only low-frequency
signals (sometimes referred to as DC "large" signals) to antenna
tuning circuit 100 (e.g., capacitor 294 serves as an AC coupler
while inductor 296 serves as a DC coupler). Power supply voltage
signal V1 may be passed to tuning circuit 100 via DC coupling path
297.
In one suitable embodiment of the present invention, power supply
voltage signal V1 that is passed to antenna tuning circuit 100 may
be modulated (toggled) using a predetermined pattern for placing
antenna tuning circuit 100 in the desired state. Power supply
voltage signal V1 may be used to configure antenna tuning circuit
100 during device startup (e.g., during power-on-reset procedures)
and may be used for powering switches and other active components
in circuit 100 during normal operation. More than one antenna
tuning circuit 100 may be coupled to signal path 45A and ground
path 45B in this way. Controlling and powering antenna tuning
circuits 100 via the existing signal path 45A allows for a simple
implementation that does not require additional power supply lines
and control lines to be formed between antenna 40 and transceiver
91.
An antenna tuning circuit 100 may include a control circuit such as
control circuit 300 and a tunable element such as tunable element
302. Control circuit 300 may provide a control signal Vc that is
used for controlling tunable element 302. In general, tunable
element 302 may be formed from one or more adjustable electrical
components. Components that may be used as all or part of circuit
302 include tunable resistive circuits,
continuously/semi-continuously adjustable inductive circuits,
continuously/semi-continuously adjustable capacitive circuits,
radio-frequency switches, and other loading circuits suitable for
provide desired impedance characteristics. Desired resistances,
inductances, and capacitances for circuit 302 may be formed using
integrated circuits, using discrete components (i.e., surface mount
technology components) and/or using dielectric and conductive
structures that are not part of a discrete component or an
integrated circuit. For example, a resistance can be formed using
thin lines of a resistive metal alloy, capacitance can be formed by
spacing two conductive pads close to each other that are separated
by a dielectric, and an inductance can be formed by creating a
conductive path on a printed circuit board.
FIG. 12 is a diagram showing one suitable circuit implementation of
antenna tuning circuit 100. Antenna tuning circuit 100 may be a two
terminal circuit having a first terminal A that may be coupled to
arm 96 and a second terminal B that may be coupled to ground G.
Voltage signal V1 may be applied across terminals A and B. As shown
in FIG. 12, control circuit 300 may include at least a low-dropout
voltage regulator 310, a comparator 314, a counter 316, and a
low-pass filter 318. Voltage regulator 310 may receive voltage
signal V1 generated from circuitry 28 via inductive DC coupler 296
(FIG. 11). Voltage regulator 310 may be operable to generate
voltage signal V2 having a constant voltage level that is lower
than the nominal positive power supply voltage level of V1, voltage
signal V3 that is a scaled-down version of voltage signal V1 (e.g.,
signal V3 will behave similarly to signal V1 but at relatively
lower voltage magnitudes), and a reference voltage signal Vref.
Signal V2 may be used to power comparator 314 and counter 316
(e.g., power supply voltage signal V2 may be supplied to these
respective circuits over path 312). Circuits 310, 314, 316, and 318
may all be coupled to terminal B so that they each have ground
path. If desired, other types of voltage regulators may be used for
generating voltage signals V2, V3, and Vref.
Comparator 314 may have a first input that is configured to receive
signal V3, a second input that is configured to receive signal
Vref, and an output. Comparator 314 may drive its output high when
the voltage level at its first input is greater than the voltage
level at its second input (e.g., comparator 314 may generate a high
output signal when V3 exceeds Vref) and may drive its output low
when the voltage level at its second input is greater than the
voltage level at its first input (e.g., comparator 314 may generate
a low output signal when V3 falls below Vref).
Counter 316 may have a control input that receives the output
signal from comparator 314. Counter 316 may, as an example, be an
edge-triggered counting circuit such as a positive-edge-triggered
counting circuit. In this example, counter 316 will count up in
response to detecting a rising edge at its control input (e.g.,
counter 316 may be used to monitor/count the number of pulses
present in signal V1). Counter 316 may also include a reset input
for receiving reset signal Vrs. Signal Vrs may be a filtered
version of signal V2 (e.g., low-pass filter 318 may be used to
filter signal V2).
For example, consider a scenario in which device 10 is initially
being powered up. During power-on-reset (POR) operations, signal V2
may initially be equal to zero volts and may be driven to a high
voltage level using voltage regulator 310 (e.g., signal V2 may be
stepped up from zero volts to a positive voltage level). When
signal V2 is low, Vrs is low and counter 316 may be placed in reset
mode having a count value of zero. When signal V2 is driven high,
Vrs will gradually be charged high and when Vrs is high, counter
315 is no longer stuck in reset mode and can now begin counting up
upon detecting rising and/or falling edges at its control
input.
Counter 316 may provide a count signal Vc reflective of its current
count value. Signal Vc may be a multi-bit digital signal or a
continuous analog signal. Tunable element 302 may be configured to
receive signal Vc via path 320. Tunable element 302 may be a three
terminal component having a first terminal that is shorted to
terminal A of antenna tuning element 100, a second terminal that
serves as terminal B for antenna tuning element 100 (e.g., a second
terminal B that is grounded), and a third terminal at which control
signal Vc is received. Tunable element 302 may be placed in a
desired operating state based on the value of signal Vc. Control
circuit 300 arranged in this way may therefore serve as control
logic that can be configured during startup to provide a desired Vc
value for adjusting tunable element 302. A single antenna 40 may
include multiple antenna tuning circuits 100, where each of these
tuning circuits may be properly adjusted so that wireless circuitry
34 may provide coverage in desired frequency bands.
The operation of antenna tuning circuit 100 is further illustrated
by the timing diagram of FIG. 13. At time t0, device 10 may be
powered up and voltage signals V1, V2, V3, and Vref may be driven
high to respective positive voltage levels (e.g., signal V1 may be
asserted to voltage level V.sub.11, signal V2 may be asserted to
voltage level V.sub.22, signal V3 may be asserted to voltage level
V.sub.31, and signal Vref may be asserted to voltage level
V.sub.rr). As shown in FIG. 13, signals V1 and V3 may be modulated
according to some predetermined pattern, whereas signals V2 and
Vref are fixed. For example, signal V1 may have a voltage level
that varies between V.sub.11 and V.sub.12 while signal V3 may have
a voltage level that varies between V.sub.31 and V.sub.32. In the
example of FIG. 13, voltage level V.sub.12 is greater than
V.sub.22, and voltage level V.sub.22 is greater than V.sub.31.
Voltage level V.sub.rr should be less than V.sub.31 but greater
than V.sub.32 so that comparator 314 will toggle its output in
response to changes in signal V3. For example, comparator 314 will
drive its output high when signal V3 is at voltage level V.sub.31
(i.e., when V3 is greater than Vref) and will drive its output low
when V3 is at voltage level V.sub.32 (i.e., when V3 is less than
Vref).
Counter 316 may keep track of a current count value whenever a
rising edge is detected at its control input (FIG. 12). The count
value will remain at zero until low-pass filtered voltage signal
Vrs rises high (at time t1). When Vrs is high, counter 316 can
begin incrementing its count value. In general, a rising edge will
be generated at the comparator output whenever signal V1 toggles
from voltage level V.sub.12 back to V.sub.11 (or whenever signal V3
rises from voltage level V.sub.32 back to V.sub.31 since V3 is
proportional to V1). As shown in the example of FIG. 13, counter
316 may count up at time t2, t3, t4, and t5 so that the final count
value is equal to four. If desired, signal V1 can be modulated
using any desired signal modulation scheme (e.g., using a
square-wave pattern as shown in FIG. 13, a sinusoidal waveform, a
sawtooth waveform, or other types of waveforms) so that counter 316
exhibits the desired count value prior to normal operation. The
resulting control signal Vc (which is proportional to the final
count value) may be used directly in controlling tunable element
302.
FIG. 14 is an illustrative lookup table 400 showing required count
values corresponding to each operating frequency band. Table 400
may contain precharacterized control values and may be stored in
storage and processing circuitry 28. As shown in FIG. 14, a count
value of two is required for operation in frequency band 1, a count
value of three is required for operation in frequency band 2, a
count value of five is required for operation in frequency band 5,
etc. Antenna tuning circuits 100 may be adjusted in parallel during
device startup based on the values of table 400. As a result, each
tuning circuit 100 should be designed such that a given count value
in look-up table 400 serves to help antenna 40 exhibit satisfactory
wireless performance in the corresponding frequency band(s).
In other suitable arrangements, each antenna tuning circuit 100 may
be adjusted individually. This implementation may require
additional control circuitry and control paths that allow control
signals to be routed individually to each antenna tuning circuit
100 during startup or during normal operation. In such
arrangements, each antenna tuning circuit 100 may have a dedicated
lookup table 400 indicating the required control value for
controlling its tunable element 302 so that the desired frequency
band is covered.
In general, element 302 may be any switchable or tunable electrical
component that can be adjusted in real time. FIG. 15 shows one
suitable circuit implementation of tunable element 302. As shown in
FIG. 15, element 302 may include a radio-frequency switch 402 and a
load circuit Z coupled in series between terminals A and B. Switch
402 may be implemented using a p-i-n diode, a gallium arsenide
field-effect transistor (FET), a microelectromechanical systems
(MEMS) switch, a metal-oxide-semiconductor field-effect transistor
(MOSFET), a high-electron mobility transistor (HEMT), a
pseudomorphic HEMT (PHEMT), a transistor formed on a
silicon-on-insulator (SOI) substrate, etc. The state of the switch
can be controlled using signal Vc generated from control circuit
300 (FIG. 11). For example, a high Vc will turn on or close switch
402 whereas a low Vc will turn off or open switch 402.
Load circuit Z may be formed from one or more electrical
components. Components that may be used as all or part of circuit Z
include resistors, inductors, and capacitors. Desired resistances,
inductances, and capacitances for circuit Z may be formed using
integrated circuits, using discrete components (e.g., a surface
mount technology inductor) and/or using dielectric and conductive
structures that are not part of a discrete component or an
integrated circuit. For example, a resistance can be formed using
thin lines of a resistive metal alloy, capacitance can be formed by
spacing two conductive pads close to each other that are separated
by a dielectric, and an inductance can be formed by creating a
conductive path (e.g., a transmission line) on a printed circuit
board.
In another suitable arrangement, tunable element 302 may include a
switch 404 (e.g., a single-pole triple-throw radio-frequency
switch) and multiple load circuits Z1, Z2, and Z3. As shown in FIG.
16, switch 404 may have ports P1, P2, P3, and P4. Terminal B of
tunable element 302 may be coupled to port P1 while terminal A of
tunable element 302 may be coupled to port P2 via circuit Z1, to
port P3 via circuit Z2, and to port P4 via circuit Z3. As described
previous, load circuits Z1, Z2, and Z3 may include any desired
combination of resistive components, inductive components, and
capacitive components formed using integrated circuits, discrete
components, or other suitable conductive structures. Switch 404 may
be controlled using signal Vc generated by control circuit 300. For
example, switch 404 may be configured to couple port P1 to P2 when
Vc is at a first value, to couple port P1 to P3 when Vc is at a
second value that is different than the first value, and to couple
port P1 to P4 when Vc is at a third value that is different than
the first and second values.
The example of FIG. 16 in which tunable element 302 includes three
impedance loading circuits is merely illustrative and does not
serve to limit the scope of the present invention. If desired,
tunable element 302 may include a radio-frequency switch having any
number of ports configured to support switching among any desired
number of loading circuits.
In another suitable arrangement, tunable element 302 may include a
variable capacitor circuit 406 (sometimes referred to as a
varactor). As shown in FIG. 16, varactor may have first terminal A,
second terminal B, and a control terminal operable to receive
signal Vc from control circuit 300. Control circuit 300 may be
adjusted so that Vc adjusts the capacitance of varactor 406 to the
desired amount. Varactor 406 may be formed using integrated
circuits, one or more discrete components (e.g., SMT components),
etc. In general, varactor 406 may be continuously variable
capacitors or semi-continuously adjustable capacitors.
FIG. 18 is a flow chart of illustrative steps for operating the
antenna tuning circuitry of the type shown in connection with FIG.
12 to cover multiple communications bands of interest. At step 500,
baseband processor 88 may select a desired frequency band for
wireless transmission/reception. At step 502, baseband processor 88
may refer to a predetermined lookup table (e.g., precomputed lookup
table 400 that is stored in circuitry 28) to obtain a count value
(M) corresponding to the selected frequency band (i.e., the count
value that counter 316 needs to exhibit so that tunable element 302
is properly tuned to support operation in the selected frequency
band).
At step 504, control circuitry 28 may drive voltage signal V1 to
zero volts and may set a temporary count variable K to zero. At
step 506, control circuitry 28 may be configured to assert signal
V1 to voltage level V.sub.11 (see, e.g., time t0 in FIG. 13).
At step 508, storage and processing circuitry 28 may check whether
K is equal to M. If K is not equal to M (i.e., if K is less than
M), control circuitry 28 may temporarily lower signal V1 to voltage
level V.sub.12 and K may be incremented by one (e.g., see, e.g., a
falling edge of signal V1 in FIG. 13). Processing may subsequently
loop back to step 506, as indicated by path 510. If K is equal to
M, the antenna tuning procedure is complete and device 10 may be
placed in normal operation to transmit and receive radio-frequency
signals in the desired frequency band(s).
In scenarios in which other operating frequency bands of interests
are needed (e.g., when device 10 moves to another geographical
region), device 10 may be automatically powered down and the steps
of FIG. 18 may be repeated to selectively tune antennas 40
according to lookup table 400 so that device 10 can operate in the
other frequency bands of interest.
The foregoing is merely illustrative of the principles of this
invention and various modifications can be made by those skilled in
the art without departing from the scope and spirit of the
invention. The foregoing embodiments may be implemented
individually or in any combination.
* * * * *